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Slide Text Space SUBMIT ALL submit all SUBMIT submit Submit Unmute volume non-standard beam consequences principles of meteorological doppler radar warning decision training division review lesson take your time and review the lesson content provided in this presentation. review lesson technical problems? if you encounter any technical problems with this lesson, please contact the rac team directly by e-mail at: nws.wdtd.rachelp@noaa.gov technical problems? complete the quiz at the end of this lesson, there is an embedded quiz. complete this quiz by selecting the best answer for each question. you need to correctly answer 70% of the quiz questions to receive completion credit in the lms. complete the quiz course completion review lesson review lesson complete the quiz technical problems? technical problems? introduction in order for nws forecasters to receive credit for this course in the nws learning center, you will need to take the following steps roadmap learning objectives identify the definition of side lobe contamination identify the most likely scenario that will exhibit side lobe contamination identify why the awips and rpg beam heights may be slightly different identify the atmospheric conditions which lead to sub-refraction, super-refraction, and ducting identify how beam height estimations will be affected by sub-refraction and super-refraction quiz! quiz! quiz! quiz! quiz! quiz! non-standard beam consequences side lobes beam heights side lobe contamination main lobe pieces of energy outside the main lobe intercept a target and return to the radar side lobe side lobe ***can occur in any direction relative to the main lobe side lobe contamination most commonly seen in the low-levels near strong horizontal reflectivity gradients aerial view main lobe main lobe side lobe side lobe side lobe contamination can occur in the vertical as well which will often manifest itself as velocity shadowing main lobe side lobe side lobe beam height calculations height arl height agl *rpg and awips heights vary slightly due to using slightly different equations **assumes standard propagation of the radar beam h = beam height above radar level j = radar elevation angle r = target’s slant range re = earth’s radius ir = index of refraction beam height: super-refraction radar beam refracts more than it would in a standard atmosphere typically caused by temperature inversions super-refracted beam standard beam ***results in overestimation of the beam height beam height: sub-refraction radar beam refracts less than it would in a standard atmosphere typically caused by dry adiabatic layers or where moisture increases with height sub-refracted beam standard beam ***results in underestimation of the beam height beam height: ducting radar beam refracts enough to hit the ground at long ranges typically caused by stable layers or sharp temperature inversions standard beam ducted beam ***results in overestimation of the beam height summary side lobe contamination occurs when pieces of energy outside the main lobe intercept a target and return to the radar most commonly seen in the low-levels near strong horizontal reflectivity gradients rpg and awips use slightly different equations to determine beam heights super-refraction typically occurs with temperature inversions sub-refraction typically occurs when moisture increases with height beam height can be over or underestimated if super-refraction or sub-refraction is occurring, respectively incorrect incorrect. awips and the rpg use slightly different forms of the beam height equation. continue continue continue continue continue continue correct correct! continue continue continue continue continue continue the awips and rpg use the exact same beam height equation. true true true true true true false false false false false false question #1 of 5 incorrect incorrect. there are no secondary transmissions and all energy transmits (and hence exists) outside the radome. continue continue continue continue continue continue incorrect incorrect. all energy transmits (and hence exists) outside the radome continue continue continue continue continue continue incorrect incorrect. the radar does not have accidental transmissions continue continue continue continue continue continue incorrect correct! continue continue continue continue continue continue side lobes are defined as _________ that exist outside the _________ which can cause erroneous echoes. pieces of energy; main lobe pieces of energy; main lobe pieces of energy; main lobe pieces of energy; main lobe pieces of energy; main lobe pieces of energy; main lobe accidental transmissions; main lobe accidental transmissions; main lobe accidental transmissions; main lobe accidental transmissions; main lobe accidental transmissions; main lobe accidental transmissions; main lobe pieces of energy; radome pieces of energy; radome pieces of energy; radome pieces of energy; radome pieces of energy; radome pieces of energy; radome secondary transmissions; radome secondary transmissions; radome secondary transmissions; radome secondary transmissions; radome secondary transmissions; radome secondary transmissions; radome question #2 of 5 incorrect incorrect. it will be very rare to see visible signs of side lobe contamination unless you have isolated supercells with strong reflectivity gradients in one or more directions. continue continue continue continue continue continue correct correct! continue continue continue continue continue continue which of the following is likely to cause side lobe contamination visible in the wsr-88d? choose all that apply strong horizontal reflectivity gradient near a supercell thunderstorm strong horizontal reflectivity gradient near a supercell thunderstorm strong horizontal reflectivity gradient near a supercell thunderstorm strong horizontal reflectivity gradient near a supercell thunderstorm strong horizontal reflectivity gradient near a supercell thunderstorm strong horizontal reflectivity gradient near a supercell thunderstorm strong vertical reflectivity gradient above the inflow region of a supercell thunderstorm strong vertical reflectivity gradient above the inflow region of a supercell thunderstorm strong vertical reflectivity gradient above the inflow region of a supercell thunderstorm strong vertical reflectivity gradient above the inflow region of a supercell thunderstorm strong vertical reflectivity gradient above the inflow region of a supercell thunderstorm strong vertical reflectivity gradient above the inflow region of a supercell thunderstorm strong horizontal reflectivity gradient within a cluster of thunderstorms far from the radar. strong horizontal reflectivity gradient within a cluster of thunderstorms far from the radar. strong horizontal reflectivity gradient within a cluster of thunderstorms far from the radar. strong horizontal reflectivity gradient within a cluster of thunderstorms far from the radar. strong horizontal reflectivity gradient within a cluster of thunderstorms far from the radar. strong horizontal reflectivity gradient within a cluster of thunderstorms far from the radar. strong vertical reflectivity gradient within an ordinary thunderstorm strong vertical reflectivity gradient within an ordinary thunderstorm strong vertical reflectivity gradient within an ordinary thunderstorm strong vertical reflectivity gradient within an ordinary thunderstorm strong vertical reflectivity gradient within an ordinary thunderstorm strong vertical reflectivity gradient within an ordinary thunderstorm question #3 of 5 incorrect incorrect. dry adiabatic layers tend to sub-refract the radar beam continue continue continue continue continue continue incorrect incorrect. dry adiabatic layers tend to sub-refract the radar beam continue continue continue continue continue continue incorrect incorrect. dry adiabatic layers tend to sub-refract the radar beam continue continue continue continue continue continue incorrect correct! continue continue continue continue continue continue which non-standard beam propagation effect most likely will occur based on this sounding shown below? sub-refraction sub-refraction sub-refraction sub-refraction sub-refraction sub-refraction super-refraction super-refraction super-refraction super-refraction super-refraction super-refraction ducting ducting ducting ducting ducting ducting standard standard standard standard standard standard question #4 of 5 incorrect incorrect. sub-refraction means beam is higher than normal, so normal equation will understimate. super-refraction means beam will be lower than normal, so normal equation will overestimate. continue continue continue continue continue continue incorrect incorrect. sub-refraction means beam is higher than normal, so normal equation will understimate. super-refraction means beam will be lower than normal, so normal equation will overestimate. continue continue continue continue continue continue incorrect incorrect. sub-refraction means beam is higher than normal, so normal equation will understimate. super-refraction means beam will be lower than normal, so normal equation will overestimate. continue continue continue continue continue continue incorrect correct! continue continue continue continue continue continue beam heights will be _____for sub-refraction, and ______ for super-refraction. underestimated; overestimated underestimated; overestimated underestimated; overestimated underestimated; overestimated underestimated; overestimated underestimated; overestimated overestimated; underestimated overestimated; underestimated overestimated; underestimated overestimated; underestimated overestimated; underestimated overestimated; underestimated as expected; underestimated as expected; underestimated as expected; underestimated as expected; underestimated as expected; underestimated as expected; underestimated underestimated; as expected underestimated; as expected underestimated; as expected underestimated; as expected underestimated; as expected underestimated; as expected question #5 of 5 completion! <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Style LeadingMargin="0" FirstLineMargin="0" Justification="Left" ListLevel="1" LineSpacingRule="Multiple" LineSpacing="20" SpacingBefore="0" SpacingAfter="0"> <ListStyle ListType="None" ListTypeFormat="Plain" Start="0" Color="#000000,00" BulletChar="•" BulletFont="Arial"> <BulletPicture Size="0x0" /> </ListStyle> </Style> <Span Text="Welcome to the Radar & Applications Course (RAC) Principles of Doppler Weather Radar. This lesson is on Non-Standard Beam Consequences. It is presented by the Warning Decision Training Division (WDTD). "> <Style FontFamily="+major" FontSize="10.5" FontIsBold="False" FontIsItalic="False" FontIsUnderline="False" FontIsStrikeout="False" ForegroundColor="dk1,00" Elevation="Normal" DisplayCase="AsIs" LinkColor="dk1,00" /> </Span> </Block> </Content> </Document> <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Style LeadingMargin="0" FirstLineMargin="0" Justification="Left" ListLevel="1" LineSpacingRule="Multiple" LineSpacing="20" SpacingBefore="4.31999969" SpacingAfter="0"> <ListStyle ListType="None" ListTypeFormat="Plain" Start="0" Color="#000000,00" BulletChar="•" BulletFont="Arial"> <BulletPicture Size="0x0" /> </ListStyle> </Style> <Span Text="Here is the complete roadmap for the “Principles of Doppler Weather Radar” section of RAC. You are currently in the WSR-88D Fundamentals portion of this section."> <Style FontFamily="+minor" FontSize="10.5" FontIsBold="False" FontIsItalic="False" FontIsUnderline="False" FontIsStrikeout="False" ForegroundColor="dk1,00" Elevation="Normal" DisplayCase="AsIs" LinkColor="dk1,00" /> </Span> </Block> </Content> </Document> <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Span Text="Here are the learning objectives for this lesson. Please take a moment to review these objectives, as the quiz at the end of this lesson is based on these objectives."> <Style FontSize="10.5" /> </Span> </Block> </Content> </Document> <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Span Text="Many of the general concepts of beam propagation are assumed to occur in a “standard” atmosphere, or we assume the beam is a rigid object. Well, the atmosphere is rarely, if ever, “standard” and the beam is not a rigid object. Click next to begin learning more about the non-standard beam consequences known as side lobes and beam height estimations."> <Style FontSize="10.5" /> </Span> </Block> </Content> </Document> <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Span Text="Recall that the initial energy for the beam is generated by the transmitter and is isotropic in nature, meaning it radiates in all directions equally. Well, that’s where the radar antenna comes into play. It focuses this energy into the 1 degree beam which is what is sent out into the atmosphere to detect the weather targets. However, the antenna doesn’t focus all of the energy into this 1 degree beam. Some of it is focused into regions just outside the main lobe called side lobes. These side lobes contain a very small fraction of the total energy transmitted but can intercept weather targets and produce returns at the radar which are strong enough to be seen on the radar display. These side lobes can occur either in the vertical or horizontal, and we’ll discuss those next. "> <Style FontSize="10.5" /> </Span> </Block> </Content> </Document> <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Span Text="Effects from side lobes are most commonly seen in the horizontal. For example, here is a typical conceptual model of a supercell thunderstorm. Once the main lobe passes by the core of the storm, the side lobe samples the core while the main lobe is sampling very low returns. Because the signal returned to the radar is dominated by the side lobe returns, that is the signal processed by the radar. However, because the radar thinks the return came from the main lobe, it places this return where the main lobe is sampling, which is just off to the side of the core in the clockwise direction. So, side lobe contamination will show up as weak reflectivity just to the side of the core. Here is an example of side lobe contamination."> <Style FontSize="10.5" /> </Span> </Block> </Content> </Document> <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Span Text="The last example of side lobe contamination was in the horizontal. However, side lobes exist in the vertical as well. The most common scenario where you will see the effects of side lobe contamination is when the main lobe is sampling the low levels, but the side lobe is sampling a fairly intense overhang. The reflectivity will not be the prominent feature, but rather the velocity signature. This is often called the velocity shadow. What happens is the velocity signature from the overhang is pretty much superimposed in the low levels. This can lead to spurious velocity couplets. Here is an example. The top two images show the low level reflectivity (left) and velocity (right). Notice the intense inbounds well away from the core, and moderate outbounds near the core, which make it appear as though there is rotation. However, stepping up in elevation, there is a strong core directly above with very strong inbound velocity. These strong inbounds aloft are basically being superimposed below because of side lobe contamination. Be aware of this limitation when viewing velocity values in weak signal areas. "> <Style FontSize="10.5" /> </Span> </Block> </Content> </Document> <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Span Text="Beam height is one factor that can cause inaccuracies in radar data. Here’s the equation which states the beam height. It’s not so important to remember the details, but you may want to take a minute to look over what each variable means to orient yourself with this equation before we move on… 
"> <Style FontSize="10.5" /> </Span> </Block> <Block> <Span Text="
"> <Style FontSize="10.5" /> </Span> </Block> <Block> <Span Text="The main thing to note here is this equation assumes a standard atmosphere for which the beam propagates through. As we all know, the atmosphere is rarely standard, so the beam will always be somewhere slightly different than the equation suggests. Also, this equation here is used by the RPG, but AWIPS uses a slightly different equation, so RPG heights and AWIPS heights may be just slightly off. "> <Style FontSize="10.5" /> </Span> </Block> </Content> </Document> <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Span Text="Let’s look at these different propagation anomalies. The first case we’ll examine is super-refraction. Super-refraction occurs when the beam bends more than normal toward the ground. This phenomenon typically occurs when there is a temperature inversion near the ground. Because the height of the beam is lower than the equation suggests the reported beam height is overestimated. Let’s look at the next case… sub-refraction."> <Style FontSize="10.5" /> </Span> </Block> </Content> </Document> <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Span Text="When the beam is sub-refracted, it bends upward a little more than normal, or is refracted a little less than normal. This type of refraction occurs when there are dry adiabatic layers or areas where moisture increases with height. Because the beam is actually higher than the equation suggests, the reported height of the beam is an underestimation. The last case we’ll look at is called ducting."> <Style FontSize="10.5" /> </Span> </Block> </Content> </Document> <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Span Text="A radar beam can sometimes get trapped in a layer and actually bend downward enough that it hits the ground at long ranges. This type of atypical propagation is called ducting. Ducting usually occurs when there are stable layers in the atmosphere or sharp temperature inversions. Because the actual beam height is lower than the equation suggests, the equation is actually overestimating the beam height. This concludes our section on beam height estimations and anomalies. "> <Style FontSize="10.5" /> </Span> </Block> </Content> </Document> <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Span Text="Let’s review what we’ve learned in this lesson. Side lobe contamination "> <Style FontSize="10.5" /> </Span> <Span Text="occurs when pieces of energy outside the main lobe intercept a target and return to the radar, and is most commonly seen in low-levels near strong reflectivity gradients. Beam height is another factor that can affect radar estimations, and RPG and AWIPS use slightly different equations to determine beam height. Super-refraction typically occurs with temperature inversions and sub-refraction typically occurs when moisture increases with height. Beam height can be over or underestimated if super-refraction or sub-refraction is occurring, respectively. Click next when you’re ready to take the quiz!"> <Style FontSize="10.5" FontIsBold="False" FontIsItalic="False" LinkColor="lt1,00" /> </Span> </Block> </Content> </Document> <Document xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Content> <Block> <Style /> <Span Text="Congratulations! You have completed this lesson. "> <Style FontSize="10.5" /> </Span> </Block> </Content> </Document>